The present invention generally relates to the technical field of N-port-receivers and particularly to a method for receiving modulated RF signals and a RF receiver comprising a N-port junction.
A six-port receiver is known acting in a direct conversion manner and allowing conversion from mm-wave range and microwave range directly to the base band. The six-port receiver detects the relative phase and relative magnitude of two incoming RF-signals by using the information of superimposed RF signals. At the same time a classic I/Q-demodulation chip (digital or analog) can be avoided. By using suitable calibration procedures the influences of, the non-ideal linear RF-components including manufacturing tolerances can be minimized. The circuitry of the six-port receiver is realized using only passive components in combination with power sensors for the detection of the relative phase and the relative magnitude of the RF-signals as shown in EP-A-0896455.
In Bossisio, Wu xe2x80x9cA six-port direct digital millimeter wave receiverxe2x80x9d, Digest of 1994 IEEE MTT Symposium, vol. 3, page 1659-1662, San Diego, May 1994, a structure for a six-port receiver is proposed.
The six-port technique has been known for its ability to accurately measure the scattering parameters, both amplitude and phase, of microwave networks. Instead of using heterodyne receivers a six-port receiver accomplishes direct measurements at microwave and mm-wave frequencies by extracting power levels at least three different ports. The imperfections of the hardware can be readily eliminated by an appropriate calibration procedure. Very accurate measurements can be made in a large dynamic range and wide frequency range. Six-port junction receivers consist of microwave components such as e.g. directional couplers and power dividers as well as power sensors. The circuit can be easily integrated as MHMIC or MMIC. The known receiver performs direct phase/amplitude demodulation at microwave and mm-wave frequencies.
By performing a calibration procedure the hardware imperfections can be readily eliminated. This significantly eases the requirement of the hardware implementation and enables the six-port receiver to operate over a wide band up to mm-wave frequencies.
According to the above cited document of Bossisio et. al. a six-port receiver concept with power dividers and 90 degrees hybrid circuits realized in distributed technology is used. The application of that known structure lies mainly in the frequency bands above 10 GHz, however, it suffers from an insufficient band width of the operation due to the inherently frequency selective nature of the 90 degree hybrid circuits.
From D. Maurin, Y.Xu, B.Huyart, K.Wu, M. Cuhaci, R. Bossisio xe2x80x9cCPW Millimeter-Wave Six-Port Reflectometers using MHMIC and MMIC technologiesxe2x80x9d, European Microwave Conference 1994, pp. 911-915, a wide-band topology for reflectometer used is known which is based on a distributing element approach featuring coplanar wave guide applications in the frequency range from 11 to 25 GHz.
From V. Bilik, et al. xe2x80x9cA new extremely wideband lumped six-port reflectometerxe2x80x9d European Microwave Conference 1991, pp. 1473-1477 and the idea of using Wheatstone Bridges and resistive structures for reflectometer applications is known.
From Li, G.Bossisio, K.Wu, xe2x80x9cDual tone Calibration of Six-Port Junction and its application to the six-port direct digital receiverxe2x80x9d, IEEE Transactions on Microwave Theory and Techniques, vol. 40, January 1996 a six-port reflectometer topology based on four 3 dB hybrid circuits, power dividers and attenuators is known.
From U.S. Pat. No. 5,498,969 an asymmetrical topology for a reflectometer structure featuring one matched detector and three unmatched detectors is known.
From U.S. Pat. No. 4,521,728 with the title xe2x80x9cMethod and six-port network for use in determining complex reflection coefficients of microwave networksxe2x80x9d a reflectometer six-port topology is known comprising two different quadrate hybrids, phase shifter, two power dividers and one directional coupler for which the realization by a microstrip line technology is disclosed.
From EP-A-0 805 561 a method for implementing a direct conversion receiver with a six-port junction is known. According to this known technique, modulated transmitted modulation is received by a direct conversion receiver which comprises a six-port junction. The demodulation is carried out analogically.
From EP-A-0 841 756 a correlator circuit for a six-port receiver is known. In this correlator circuit the received signal is summed up with a local oscillator signal at various phase angles, wherein the phase rotation between the local oscillator and RF signals is carried out separately from the summing of the correlator outputs.
Generally, when applying the N-port-technique as said forth above for receive a modulated RF signal, two RF signals are set to the N-port junction. In the case of a coherent reception and detection one of the supplied RF signals originates from a local oscillator. Particularly in the case of using a local oscillator for a coherent detection the following problems can arise:
The local oscillator signal (or generally spoken the second RF signal) passing through the end port junction arrives at the first RF input and can propagate further to the antenna or a preamplifier stage, is reflected there and approaches then the first RF input of the N-port junction together with the RF signal to be demodulated. Obviously this may produce demodulation errors.
In the case the N-port junction is a junction with five or more ports, there are cases that the power level detection of the RF signal to be demodulated alone is required. In such a case it is important that no local oscillator signal (generally RF signal from the second RF input of the end port junction) arrives at the power sensor to not disturb the demodulation.
In view of the prior art it is therefore the object of the present invention to provide for a RF reception technology on the basis of a N-port junction dealing with the above cited problems. In other words, with a technique according to the present invention it should be possible to avoid as far as possible unwanted influences of the RF signal from the second input (LO signal) on the power detection.
This object is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the present invention.
According to the present invention therefore a method for receiving modulated RF signals is proposed. A first RF signal is set to a first input of a N-port junction. N thereby is an integer larger than two. The N-port junction can be preferably a three port, four port, five port or six port junction. A second RF signal is set to a second input of the N-port junction. Nxe2x88x922 output signals of the N-port junction are supplied to power sensors for further processing. According to the invention the first input is (RF) isolated from the second input by means of a non-reciprocal two-port isolation unit.
The non-reciprocal two-port isolation unit can be an active circuitry.
Particularly in the case of a coherent reception/detection, the second RF signal can originate from a local oscillator.
According to the present invention furthermore a RF receiver for modulated RF signals is proposed. The RF receiver comprises a N-port junction, N being an integer larger than two. The N-port junction is supplied to the first RF signal in the first input and with the second RF signal in the second input. The receiver furthermore comprises an isolation block comprising a non-reciprocal two-port isolation unit for (RF) isolating the second input from the first input.
The non-reciprocal two-port isolation unit can be an active circuitry.
The active circuitry can be an amplifier.
The isolation block can furthermore comprise at least one passive circuitry providing for a resistive or reactive matching.
The isolation block can comprise resistive attenuators.
The N-port junction can comprise at least one of a three-port junction and a four-port junction and the isolation block in this case is connected between one of the first and second input of the N-port junction and the at least one of three-port junction and the four-port junction.
The N-port junction can comprise at least two three-port junctions and the isolation block in this case can be connected between the two three-port junctions.
The N-port junction can comprise at least one three-port junction and at least one four-port junction, in which case the isolation block is connected between a three-port junction and a four-port junction.
The N-port junction can comprise at least one phase shifter.